(i) Field of the Invention
The present invention relates to a method for preparing molded articles of a crosslinked polyolefin by allowing a crosslinking reaction to occur at the time of the molding of a polyolefin.
(ii) Description of the Prior Art The crosslinking of a polyolefin is utilized for various purposes such as for improving physical properties such as heat resistance and mechanical strength of the molded articles of the polyolefin and for improving the fluidity of the polyolefin at the time of foaming in the manufacturing process of molded articles of a foamed polyolefin. As a crosslinking process, there have been known a process in which a bifunctional monomer and a radical polymerization initiator are mixed with a polyolefin and the mixture is then heated, melted and molded to achieve the crosslinking, a process in which the molded polyolefin is irradiated with radiation to achieve the crosslinking, and a process in which a modified polyolefin having a hydrolyzable alkoxysilane group in its molecule is molded and then treated with boiling water to carry out hydrolysis, whereby an Si-O-Si bond is formed and thus the crosslinking is achieved (e.g., Japanese Patent Application Laid-open No. 58-117244).
Of these conventional techniques, the process using the bifunctional monomer has the problem that unreacted monomer tends to remain, and the process in which the crosslinking is achieved by the treatment after the molding is complex. Furthermore, the process in which the polyolefin is irradiated with radiation is scarcely applied to thick molded articles, and the process which comprises forming the Si-O-Si bond from the hydrolyzable alkoxysilane group by the hydrolysis reaction to achieve the crosslinking has the problem that the molded articles are poor in water resistance. Accordingly, it has been desired to develop an easy crosslinking process without the problem that unreacted monomer remains.